1. Field of the Invention
This invention relates to the operation of transit doors.
2. Description of Related Art
There are several conventional approaches to vehicular door systems (of the type typically used in bus or rail mass-transit systems). Commonly used approaches include the following.
Swing doors: These are simple double panel doors which swing outward.
Slide-glide doors: Alternatively known as “inward retracting” doors, slide-guide doors have a mechanism that rotates the double door panels outward (similarly to the “swing doors”) but simultaneously retract the door panels into the vehicle. The ideal result is that the door panels are seated flat against the entryway perimeter but with the interior surface of the doors exposed rather than the outside surface (allowing handrails and other “interior” hardware to be accessible when the vehicle is stopped and the doors are in the open position, but not exposed on the exterior of the vehicle when the vehicle is in operation).
In each type of door, along each vertical door frame is positioned driven door shafts which through various linkages drive the opening and closing of the adjacent door panels. A number of transit buses have a significant curve back at the top of the front end of the bus such that the upper end of the forward most door panel must also be curved back. In the past, in order to accommodate the curve back of the door, the driven door shaft is comprised of two offset vertical drive shafts 20, 21 joined by an intermediate shaft 23 that has universal joints 24, 25 at each end as shown in FIG. 1. The intermediate shaft 23 has a sliding spline 26 on one end that interfaces a complementary spline on one of the universal joints. This allows the two universal joints to be installed at various distances from each other, thereby accounting for the production tolerances present in the frame of the bus. Arms 27 fixed to the drive shafts 20 operate the door panels to open and close.
There are also situations wherein rectangular doors have two coaxial drive shafts due to the configuration of the walls adjacent the door and/or obstructions between the upper and lower shafts.
Referring to FIG. 2, a rotary actuator 30 drives connecting rods 31, 32 which drive door shaft levers 33, 34 to open and close the doors.
Unfortunately, each universal joint and the spline connection are sources of backlash which must be accounted for in the design of the door. Moreover, each of these elements must be periodically lubricated.